Relativistic Coupled Cluster with Completely Renormalized and Perturbative Triples Corrections

We
have implemented noniterative triples corrections to the energy
from coupled-cluster with single and double excitations (CCSD) within
the 1-electron exact two-component (1eX2C) relativistic framework.
The effectiveness of both the CCSD(T) and the completely renormalized
(CR) CC(2,3) approaches are demonstrated by performing all-electron
computations of the potential energy curves and spectroscopic constants
of copper, silver, and gold dimers in their ground electronic states.
Spin–orbit coupling effects captured via the 1eX2C framework
are shown to be crucial for recovering the correct shape of the potential
energy curves, and the correlation effects due to triples in these
systems change the dissociation energies by about 0.1–0.2 eV
or about 4–7%. We also demonstrate that relativistic effects
and basis set size and contraction scheme are significantly more important
in Au2 than in Ag2 or Cu2.